After months of controversy, the journal Nature has published the details of an experiment…
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As scientists scramble to determine if the new virus poses a threat to humans, others suggest this is a good opportunity to study an epidemic in progress, to help us prepare for the Big One.

And indeed, the spread of the flu to seals provides a real-life example of what scientists have been predicting could happen with H5N1. Last fall, 162 dead harbor seal pups washed up on the shores of New Hampshire and Massachusetts. Analysis of the dead seals indicated that they had been killed by a virus that was spreading from seal to seal — proof that the bird flu had mutated into something new.

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The question now is, does this flu pose a threat to humans? Writing in the New York Times, Carl Zimmer explores the possibility:

A new strain that can spread among seals is a reason for serious concern, Dr. [Simon] Anthony said. "What we fear is that it would allow the virus to persist within the seal population," he said. "And if it persists, who knows what other changes may accumulate over time?"

"If it adapts better to mammal hosts, it may well start to move into humans," Dr. Lipkin said. "This is clearly a virus for which we need some surveillance."

Pigs, Dr. Lipkin noted, are especially good at producing new flu strains because they can be infected by bird flu and mammal flu at the same time. Two kinds of virus can combine, giving rise to new hybrid strains.

Dr. Lipkin and his colleagues found evidence that seal cells can also be invaded by both kinds of viruses - raising the possibility that they could produce new hybrid flu strains as well.

"It could be the equivalent of an aquatic pig," Dr. Lipkin said.

Dr. Holmes wanted to see more evidence for the idea that flu viruses can mix in seals. He also pointed out that H3N8 has never crossed from dogs or horses to people.

"Just because we find a seal with mammal-adapted H3N8 does not mean we're going to get a human pandemic," Dr. Holmes said. "At the moment, it's hard to say what the threat really is."